The present invention relates to an improved cooling apparatus of the cold plate type. Cold plates are a very old apparatus whereby melting ice is used to cool liquids circulated through tubing in thermal contact with the ice. For the particular application of cooling and dispensing beverages, a typical design would be to have coils of tubing carrying carbonated water, plain water, and beverage syrup running through an aluminum block. The aluminum block is what is referred to as a cold plate and is located at the bottom of an ice storage container. The coils of water and syrup are routed to appropriate mixing valves where the beverage is dispensed. The ice storage container thus serves the dual purpose of storing ice to dispense with the beverage and containing ice which absorbs heat from the cold plate.
The physical principle upon which a cold plate operates is simply that of using the melting ice as a heat sink which absorbs heat from the water and syrup as they flow through the cold plate. That is, heat flows from the water and syrup to the top of the cold plate upon which rests a quantity of ice. Rather than raising the temperature, the transferred heat effects a phase change of the ice from solid to liquid. The heat is, thus, absorbed as latent heat rather than raising the temperature of the heat sink. In this way, the heat capacity of the heat sink is greatly increased over what it would be if, for example, liquid water cooled to a freezing temperature were used as a heat sink.
As heat is transferred to the ice and melting occurs, however, a quantity of water is produced in the ice storage container above the cold plate. This water tends to inhibit the direct transfer of heat to the ice where the heat can be absorbed as the latent heat of melting. That is, the heat must first raise the temperature of the water slightly before the heat can be transferred to the ice. The resulting lower temperature differential retards the further flow of heat. Any water between the ice and the surface of the cold plate thus acts as an insulator. It is an object of the present invention to provide a means for minimizing the interposition of water between the ice and beverage coils in a cold plate apparatus.
Another problem associated with accumulated water above the cold plate is the occurrence of "bridging" when a portion of the ice melts, liquid water accumulates between the ice and the cold plate. If the liquid water is not immediately removed, the layer of liquid tends to enlarge by the addition of more melted ice until hydrostatic pressure forces the liquid toward a drain. After the liquid is drained, however, there is left a gap between the ice and the cold plate where the ice "bridges" over the area vacated by the liquid water. Since no ice is contacting the cold plate over this area, the cooling efficiency of the cold plate is severely diminished. U.S. Pat. No. 4,617,807 discloses a cold plate apparatus designed to overcome this problem by incorporating involute beverage coils. Since most of the heat transfer, and thus melting of ice, occurs over the area of the cold plate nearest the inlets of the beverage coils where the beverage is warmest, the '807 apparatus uses involute coils to provide for more uniform heat transfer and less accumulated water over any one area of the cold plate. This method of dealing with bridging problems, however, compromises the efficiency of the cold plate. The total heat transfer from beverage to ice is maximized by separating the warmer beverage from the colder beverage by as much distance as possible as the beverage flows through the coils within the cold plate. It is a further object of the present invention to provide a means for preventing accumulations of water which would cause bridging of ice but without compromising the cooling efficiency of the apparatus.
Another factor influencing the efficiency of a cold plate apparatus is the surface area of the beverage coils exposed to the cooling surface of the cold plate. It is a further object of the present invention to maximize the surface area of the beverage coils exposed to the cold plate.
A still further object of the present invention is to configure the beverage coils so that the inlet and outlet coil fittings are easily accessible during installation and repair.